1. Field of the Invention
This invention relates to a light-receiving member, an image-forming apparatus and an image-forming method. More particularly, it relates to a light-receiving member having a photosensitive layer used to form an electrostatic latent image thereon, an image-forming apparatus having the light-receiving member, and an image-forming method making use of the light-receiving member.
2. Related Background Art
(1) Image-Forming Apparatus
A number of methods as disclosed in U.S. Pat. Nos. 2,297,692, 3,666,363 and 4,071,361 are conventionally known as electrophotography. In general, copies are obtained by forming an electrostatic latent image on an light-receiving member (e.g., an electrostatic latent image bearing member) by utilizing a photoconductive material and by various means, subsequently developing the latent image by the use of a toner to form a toner image, transferring the toner image as a developed image to a transfer medium such as paper as occasion calls, and then fixing the toner image by the action of heat, pressure, or heat and pressure, or solvent vapor. In the course of the foregoing, untransferred toner remains on the light-receiving member even after the toner image has been transferred to the transfer medium, and hence such untransferred toner has ever been collected through a cleaning step and put away outside the system as waste toner.
With an increase in the throughput of information in recent years, there is a more increasing demand for image-forming apparatus such as copying machines and laser beam printers having a large copying volume (i.e., large-sized high-speed machines).
As light-receiving members, light-receiving member performances adapted to high-speed are required to be improved. At the same time, in these days where more minute image quality is demanded, toners have been directed toward smaller particle diameters, not to speak of improvements in light-receiving member performances, and those having a weight-average particle diameter of from 5 to 11 xcexcm as measured by COULTER Counter or the like are in wide use.
Meanwhile, in order to improve cleaning performance, contrived are a blade with grooves as disclosed in Japanese Patent Application Laid-open No. 54-143149 and a blade with projections as disclosed in Japanese Patent Application Laid-open No. 57-124777. These publications, however, do not refer to any cleaning system suited for image-forming apparatus having a process speed of 400 mm/sec or higher and comprising a fine-particle toner improved in fixing performance and an a-Si (amorphous silicon) light-receiving member.
FIG. 1 is a schematic view for describing an example of an image-forming process in a copying machine which is a kind of the image-forming apparatus. Here is given a diagrammatic cross-sectional view of the construction of the image-forming apparatus.
A light-receiving member 101 is rotated in the direction of an arrow X. The light-receiving member 101 is formed in a drum, and is provided with a sheet-like inner-surface heater 123 on the drum inside, by means of which the light-receiving member 101 is temperature-controlled. Around the light-receiving member 101, it is provided with a charging means primary charging assembly 102, an electrostatic latent image forming portion 103, a developing means developing assembly 104, a transfer paper feed system 105, a transfer means transfer charging assembly 106(a), a separation charging assembly 106(b), a cleaner 125, a transport system 108 and a destaticizing light source 109.
An image-forming process is described below by further giving a specific example. The light-receiving member 101 is uniformly electrostatically charged by means of the primary charging assembly 102, to which a high voltage of from +6 to +8 kV is kept applied. Light emitted from a halogen lamp 110 reflects from an original 112 placed on an original glass plate 111 and travels via mirrors 113, 114 and 115, and an optical image is formed by a lens 118 of a lens unit 117. The optical image is guided via a mirror 116 to the electrostatic latent image forming portion and projected on the light-receiving member 101, thus an electrostatic latent image is formed on the light-receiving member 101. To this latent image, a toner for developing electrostatic latent images is supplied from the developing assembly 104, and the latent image is formed into a developed image made visible (hereinafter also xe2x80x9ctoner imagexe2x80x9d).
Meanwhile, a transfer material P is fed toward the light-receiving member 101 via the transfer paper feed system 105 while its leading end is timing-controlled by means of a registration roller 122. To the transfer material P, an electric field having a polarity opposite to that of the toner is imparted from the side of the transfer charging assembly 106(a) at a gap formed between the transfer charging assembly 106(a) to which a high voltage of from +7 to +8 kV is kept applied and the light-receiving member 101. Thus, the toner image held on the surface of the light-receiving member 101 is transferred to the transfer material P. The transfer material P is separated from the light-receiving member 101 by means of the separation charging assembly 106(b), to which a high AC voltage is kept applied at a peak-to-peak voltage of from 12 to 14 kVp-p and a frequency of from 300 to 600 Hz, and is made to pass the transport system 108 to come to a fixing assembly 124. The transfer material P is, after the toner image held thereon has been fixed by means of the fixing assembly 124, delivered outside the apparatus.
The toner remaining on the light-receiving member 101 is removed from the surface of the light-receiving member 101 by means of a cleaning roller 107 and a cleaning blade 121 which are provided in the cleaner 125. Any electrostatic latent image remaining on the surface of the light-receiving member 101 is eliminated by means of the destaticizing light source 109
(2) Light-Receiving Member
With regard to techniques for device members used in the light-receiving member, various materials are proposed, such as selenium, cadmium sulfides, zinc oxide, phthalocyanine and amorphous silicon (hereinafter xe2x80x9ca-Sixe2x80x9d). In particular, non-single-crystal deposited films composed chiefly of silicon atoms as typified by a-Si films, e.g., amorphous silicon deposited films of a-Si compensated with hydrogen and/or a halogen (e.g., fluorine or chlorine) are proposed for light-receiving members having high performance and high durability and causing no environmental pollution, and some of them have put into practical use. As processes for forming such deposited films, a large number of processes are conventionally known, such as sputtering, a process in which material gases are decomposed by heat (heat-assisted CVD), a process in which material gases are decomposed by light (photo-assisted CVD), and a process in which material gases are decomposed by plasma (plasma-assisted CVD). In particular, plasma-assisted CVD, i.e., a process in which material gases are decomposed by glow discharge that utilizes a direct-current or high-frequency (RF or VHF) power or a microwave power to form a thin-film deposited film on an insulating substrate made of glass or quartz or formed of a heat-resistant synthetic resin film, or a substrate having been conductive-treated by providing a metal on the surface of any of these, or a conductive substrate made of stainless steel or aluminum, is preferred in the formation of non-single-crystal silicon films, preferably a-Si deposited films, for light-receiving members.
Proposals are made in variety in order to improve electrophotographic performance of light-receiving members having a photosensitive layer formed of amorphous silicon. For example, Japanese Patent Application Laid-open No. 57-115551 discloses an example of a light-receiving member comprising a photoconductive layer constituted of an amorphous material composed chiefly of silicon atoms and containing at least one of hydrogen atoms and halogen atoms, and provided thereon with a surface barrier layer constituted of a non-photoconductive amorphous material composed chiefly of silicon atoms and carbon atoms and containing hydrogen atoms.
Japanese Patent Application Laid-open No. 61-219961 also discloses an example of a light-receiving member constituted of an a-Si type photosensitive layer and formed thereon as a surface protective layer an a-C:H (amorphous carbon) film containing 10 to 40 atom % of hydrogen atoms.
Japanese Patent Application Laid-open No. 6-317920 discloses a process for producing, using a high-frequency power having a frequency of 20 MHz or higher, a light-receiving member constituted of a photoconductive layer formed of a non-single-crystal silicon material composed chiefly of silicon atoms and an a-C:H surface protective layer containing 8 to 45 atom % of hydrogen atoms.
European Patent Publication No. 154160 also discloses a method, and an apparatus, for forming a light-receiving member device having a top blocking layer formed by microwave plasma-assisted CVD using a microwave power (e.g., frequency: 2.45 GHz) as a material gas decomposition source.
These techniques have brought about improvements in electrical, optical and photoconductive performances as well as service environmental properties and running performance, and also have enabled improvement in image quality level.
However, in recent years, image-forming apparatus are demanded to have much higher performances and much longer service life. Under such circumstances, even image-forming apparatus having ever exhibited sufficient performances have had to be put to studies in some cases, depending on service environment and prerequisite image quality.
For example, as mentioned previously, with an increase in the throughput of information in recent years, there is a more increasing demand for image-forming apparatus such as copying machines and laser beam printers having a large copying volume (i.e., large-sized high-speed machines). In other words, image-forming apparatus are increasingly being made high-speed. In image-forming apparatus having been thus made high-speed, the capability of fixing toner images to transfer materials depends on how the toner images on transfer materials are heated in a fixing assembly. In achievement of high speed, the temperature of the fixing assembly must be made higher as the time for which a transfer material passes the inside of the fixing assembly is shorter. This causes an increase in the power consumption in the fixing assembly which already occupies about 80% of power consumption of the whole image-forming apparatus.
Even under such circumstances, the reduction of power consumption as commercial needs is an important subject. Accordingly, the fixing performance of toners themselves is being improved so that a good fixing performance can be attained even without making the fixing assembly have so much a high temperature. Also, not only in high-speed light-receiving member but also in medium-speed to low-speed light-receiving member, efforts on energy saving and resource saving are continually made from every aspect as a part of countermeasures for ecology. As one of them, it is attempted to achieve power saving of fixing assemblies. In this case, too, well fixable toners having a good fixing performance even at a temperature lower than conventional toners are also on development so that good fixing performance can be attained even when the fixing assembly is operated at a low temperature.
Such well fixable toners contain low-melting materials (such as binder resin and/or wax), and are so designed as to melt and fix well even when fixed at a relatively low temperature. When such well fixable toners are used, sufficient performance is achievable in practical use with regard to image quality and fixing performance. However, their low-melting properties may also act on the surface of the light-receiving member to cause a side effect that the toner melt-adheres to the surface of the light-receiving member.
What is meant by xe2x80x9cmelt-adherexe2x80x9d is that the toner melts to come to adhere to the surface of the light-receiving member during its service over a long period of time. Depending on the degree of adhesion, marks of melt-adhesion may appear on solid white images or halftone images, resulting in a difficulty in practical use. Where such melt-adhesion has occurred and its marks have appeared on images, a service person must go to a client to perform maintenance service, requiring an expense. Also, since the light-receiving member is detached from the main body of a light-receiving member to perform the maintenance service, there is a possibility that the light-receiving member is struck against something during the maintenance service to become unserviceable. Such a phenomenon of melt-adhesion may occur frequently, depending on any combination of environment in which the image-forming apparatus is used, components contained in the toner, surface properties of the light-receiving member, pressure at which the cleaner is brought into pressure contact, process speed and so forth.
As also mentioned previously, as light-receiving members, light-receiving member performances adapted to high-speed are required to be improved, and also, in these days where more minute image quality is demanded, toners have been directed toward smaller particle diameters, not to speak of improvements in light-receiving member performances, and those having a weight-average particle diameter of from 5 to 8 xcexcm as measured by COULTER Counter or the like are in wide use. However, having a small particle diameter is also a trend that is disadvantageous for the melt-adhesion. Hence, in order to improve the capability of making the toner adhere to the light-receiving member with difficulty or of scraping off any toner having adhered thereto, a countermeasure must be taken such that the blade is made to have a high hardness or brought into pressure contact at a higher pressure.
However, making the blade have a high hardness brings the blade properties from rubbery condition into glassy condition, and hence the blade tends to abrade the light-receiving member. Once such abrasion has occurred, in the case of a-Si type high-hardness light-receiving members, the surface may be abraded unevenly to cause stripe-like uneven abrasion, which may appear on images when images are formed. Accordingly, it is desirable to use the a-Si type light-receiving member under conditions that may cause no abrasion of the surface.
As another method of preventing the melt-adhesion, in some cases silica or the like is added to the toner itself as an abrasive, is used to modify components or is used in a larger quantity. Incorporation of an abrasive in the toner itself provides a higher capability of rubbing the drum (light-receiving member) surface and hence makes any molten toner adhere thereto with difficulty. This can prevent the melt-adhesion on the one hand, but on the other hand still strengthens the force of rubbing the light-receiving member surface as a side effect. Hence, it is difficult to balance these so as to only prevent the melt-adhesion without the abrasion of the light-receiving member surface.
As stated previously, after images such as copied images have been formed using the image-forming apparatus such as an electrophotographic apparatus, the toner remains partly on the outer periphery of the photosensitive member light-receiving member, and hence such residual toner must be removed. Such residual toner may be removed by a cleaning step making use of, besides the cleaning blade described previously, a fur brush, a magnet brush or the like.
However, the toner having a small average particle diameter, used for the achievement of higher image quality of printed images in recent years, makes it difficult to remove the residual toner completely in the above cleaning step, too. This may cause a problem of toner adhesion that, as a result of repeated copying, the residual toner clings or melt-adheres to the photosensitive member surface to cause faulty images in the form of black spots on white background images.
As a countermeasure for solving the above problem, an approach thereto is also made from the aspect of the light-receiving member. As disclosed in Japanese Patent Application Laid-open No. 9-297420, a method is available in which, in a photosensitive member using amorphous silicon to form a photosensitive layer, the surface of a conductive substrate on which the photosensitive layer is to be formed by film formation is previously roughed by cutting or by means of a rotary ball mill. In this case, the substrate surface is defined by the value of macroscopic surface roughness measured with a surface profile analyzer.
Japanese Patent Application Laid-open No. 8-129266 also defines a value of surface roughness Ra, which, however, defines the shape of a conductive substrate worked, and the substrate surface is defined by the value of macroscopic surface roughness measured with a surface profile analyzer.
In recent years, however, with progress of digitization of electrophotographic apparatus, it is becoming predominant to form latent images using a light source composed chiefly of a single wavelength. As the result, the method proposed above in which the substrate is previously cut may have a problem that an interference pattern ascribable to the substrate surface configuration appears on printed images. Also, it may result in a cost increase to additionally provide the step of roughing the conductive substrate surface previously. Conversely, the working of a substrate in a roughness that may cause no interference pattern may make it impossible to well keep the toner adhesion from occurring.
The present invention was made taking account of the above various points. Accordingly, an object of the present invention is to provide a light-receiving member, an image-forming apparatus and an image-forming method which enable stable formation of images over a long period of time.
Another object of the present invention is to provide a light-receiving member, an image-forming apparatus and an image-forming method which are widely applicable to high-speed machines and also to medium-or low-speed machines, promising a low power consumption and an overall low burden to environment.
Still another object of the present invention is to provide a light-receiving member, an image-forming apparatus and an image-forming method which enable formation of images in so high an image quality as to be free from, or substantially not problematic on, any faulty images due to melt-adhesion or filming without dependence on environment.
A further object of the present invention is to provide an image-forming apparatus having a superior running performance, which can always form sharp images without causing any wear which is causative of scratches on the light-receiving member or faulty images even when used over a long period of time.
In addition, a still further object of the present invention is to provide a light-receiving member, an image-forming apparatus and an image-forming method which enable formation of good images, preventing the toner adhesion at the time of cleaning.
As stated previously, in order to ensure fixing performance when the image-forming apparatus is driven at a higher speed or the fixing assembly is operated at a lower temperature, low-melting well fixable toners are being on development. However, where such toners are used on conventional a-Si light-receiving members, the problem of melt-adhesion or filming may occur when used over a long period of time. Also, extensive studies are made on cleaning conditions relating closely to the prevention of melt-adhesion or filming. However, any cleaning set under conditions that can perfectly prevent the melt-adhesion may conversely cause the stripe-like abrasion of the light-receiving member surface when used over a long period of time. In such a case, there is a problem that the stripe-like abrasion appears on halftone images surface to directly result in troubles on image quality.
We have made extensive studies on whether or not this problem, caused when a higher speed and a lower power consumption are to be achieved on image-forming apparatus, can be solved by improving surface properties of the light-receiving member. As a countermeasure therefor, a method can be contemplated in which, e.g., the outermost surface of the light-receiving member is made more readily slippery so as to prevent the melt-adhesion or filming and at the same time made harder so as to prevent the scratches and wear. Studies made on any materials most suited for such a purpose have revealed that particularly an amorphous carbon film containing hydrogen (hereinafter xe2x80x9ca-C:H filmxe2x80x9d) is most suitable. This a-C:H film, as being also called diamond-like carbon (DLC), has a very high hardness and also a peculiar solid lubricity, and hence this is considered to be a material most suited for use in such a purpose.
Accordingly, the present inventors made extensive studies on the extent to which the melt-adhesion or filming may occur when the light-receiving member making use of the a-C:H in the surface layer is used in combination with the well fixable toners. As the result, expectedly a remarkable effect was seen in the prevention of the melt-adhesion or filming, compared with conventional surface layers making use of a-SiC. It, however, was not the case that the effect was sure. For example, when applied to apparatus having a very high process speed as in the case of very high-speed image-forming apparatus, the melt-adhesion or filming still occurred in some cases. The cause thereof is unclear, and is presumed as follows: With an increase in process speed of an image-forming apparatus, the relative speed of the cleaner portion and light-receiving member increases relatively. In such a case, even though the a-C:H film has a solid lubricity, a frictional force still acts more or less. As a mechanism for the cleaning of the light-receiving member making use of a-Si, cleaning blades are commonly used, where there is a possibility that the cleaning blade stands chattered when the apparatus is driven at a high speed. Where such chattering occurs, the effect of compression between the cleaning blade and the light-receiving member surface becomes higher, so that the toner is strongly pressed against the light-receiving member surface to come to tend to cause the melt-adhesion or filming, as so presumed.
To solve this problem, the present inventors made further studies. As the result, it has been revealed that the rate of occurrence of the melt-adhesion or filming correlates with the surface roughness of the outermost surface of a surface layer such as an a-C:H surface layer.
Nevertheless, it has been discovered that the effect of preventing toner adhesion does not necessarily depend on the macroscopic substrate surface roughness measured with a surface profile analyzer and is rather governed by a microscopic surface roughness peculiar to amorphous silicon films.
With regard to the relationship between the surface roughness and the melt-adhesion or the like, goods results were obtainable when the surface layer is in a surface roughness Ra of 15 nm or more where the reference length is set to be 10 xcexcm. What is meant by the fact that the surface layer has a surface roughness not smaller than a suitable size is that the part where the surface layer comes into contact with the cleaning blade stands in point contact when viewed microscopically, thus the frictional force is reduced there, as so considered. As the result, the cleaning blade may less chatter to strongly prevent the melt-adhesion from occurring, as so considered. On the other hand, however, the melt-adhesion or filming was seen to tend to conversely occur at a higher rate when the surface roughness Ra was beyond 100 nm. The cause thereof is still a matter of presumption. Where the light-receiving member surface is too uneven, its hills may collide against the cleaning blade conversely, and the toner is compressed there to tend to cause the melt-adhesion or filming. Such a condition has probably been brought about, as so presumed.
The present invention provides a light-receiving member comprising a conductive substrate, and formed superposingly thereon a photosensitive layer and a surface protective layer in order, wherein;
the light-receiving member has a surface roughness Ra of from 15 nm to 100 nm.
The present invention also provides an image-forming method comprising the step of rendering visible an electrostatic pattern formed on a light-receiving member having the above surface roughness Ra, by the use of a toner containing at least a binder resin, a charge control agent and a wax, and having a weight-average particle diameter of from 3 xcexcm to 11 xcexcm; the binder resin having a Tg (glass transition temperature) of from 40xc2x0 C. to 80xc2x0 C., and the wax having a main peak in the region of molecular weight of from 400 to 10,000 and having at least one endothermic peak in the region of from 60xc2x0 C. to 150xc2x0 C. at the time of heating in differential thermal analysis.
The present invention still also provides an image-forming apparatus comprising;
a light-receiving member for holding thereon an electrostatic latent image;
a charging means for applying a voltage to a charging member to charge the light-receiving member;
an electrostatic-latent-image-forming means for forming the electrostatic latent image on the light-receiving member thus charged;
a developing means for forming a developed image on the light-receiving member by causing an electrostatic-latent-image-developing toner carried on a toner-carrying member, to move to the electrostatic latent image formed on the light-receiving member;
a transfer means for electrostatically transferring the developed image formed on the light-receiving member, to a transfer material via, or not via, an intermediate member; and
a fixing means for fixing to the transfer material the developed image held thereon;
the light-receiving member being a light-receiving member comprising a conductive substrate, and formed superposingly thereon a photosensitive layer and a surface protective layer in order;
the surface protective layer comprising non-single-crystal carbon containing from 35 atom % to 55 atom % of atoms selected from the group consisting of hydrogen atoms and halogen atoms, and having a surface roughness Ra of from 15 nm to 100 nm; and
the photosensitive layer comprising a non-single-crystal material composed chiefly of silicon atoms and containing atoms selected from the group consisting of hydrogen atoms and halogen atoms; and
the toner containing at least a binder resin, a charge control agent and a wax, and having a weight-average particle diameter of from 3 xcexcm to 11 xcexcm; the binder resin having a Tg (glass transition temperature) of from 40xc2x0 C. to 80xc2x0 C., and the wax having a main peak in the region of molecular weight of from 400 to 10,000 and having at least one endothermic peak in the region of from 60xc2x0 C. to 150xc2x0 C. at the time of heating in differential thermal analysis.
The present invention further provides an image-forming method comprising;
a charging step of applying a voltage to a charging member to charge a light-receiving member;
an electrostatic-latent-image-forming step of forming an electrostatic latent image on the light-receiving member thus charged;
a developing step of forming a developed image on the light-receiving member by causing an electrostatic-latent-image-developing toner carried on a toner-carrying member, to move to the electrostatic latent image formed on the light-receiving member;
a transfer step of electrostatically transferring the developed image formed on the light-receiving member, to a transfer material via, or not via, an intermediate member; and
a fixing step of fixing to the transfer material the developed image held thereon;
the light-receiving member being a light-receiving member comprising a conductive substrate, and formed superposingly thereon a photosensitive layer and a surface protective layer in order;
the surface protective layer comprising non-single-crystal carbon containing from 35 atom % to 55 atom % of atoms selected from the group consisting of hydrogen atoms and halogen atoms, and having a surface roughness Ra of from 15 nm to 100 nm; and
the photosensitive layer comprising a non-single-crystal material composed chiefly of silicon atoms and containing atoms selected from the group consisting of hydrogen atoms and halogen atoms; and
the toner containing at least a binder resin, a charge control agent and a wax, and having a weight-average particle diameter of from 3 xcexcm to 11 xcexcm; the binder resin having a Tg (glass transition temperature) of from 40xc2x0 C. to 80xc2x0 C., and the wax having a main peak in the region of molecular weight of from 400 to 10,000 and having at least one endothermic peak in the region of from 60xc2x0 C. to 150xc2x0 C. at the time of heating in differential thermal analysis.